A new study reveals that an older sister's pregnancy increases a teen girl's risk of getting pregnant herself — and the effect is stronger than that of education.

According to the Telegraph, a study of Norwegian women who had kids in the seventies and eighties shows that an older sister who got pregnant doubled a teenager's chances of pregnancy. Closeness in age and family poverty increased the risk even further. And while more education reduces this risk, study author Carol Popper says, "these findings reveal the positive sibling effect still dwarfs the negative effect of education."

The rumored "pregnancy pact" in Gloucester, MA sparked fears that girls might reinforce one another's desire to become teen mothers, and the possibility that conditions from obesity to happiness may be contagious has been much discussed lately. It's certainly possible that having an older sister get pregnant makes early sexual activity, unprotected sex, or teen motherhood seem more acceptable to teen girls. However, it's also possible that girls who get pregnant come from families where birth control isn't discussed or encouraged. And it's not clear whether these influences have changed since the late twentieth century, when the data was gathered. At the very least, though, the study authors say their research points to the need for targeted anti-pregnancy programs — and educating teen girls about how to prevent unwanted pregnancy is always a good idea.